This invention relates generally to a dust collector for removing air from a ventilation duct and in particular to a collector which will remove dust without the use of water sprays.
Underground coal mines must be ventilated to reduce methane concentrations to a safe level. One of the more successful ventilation methods has utilized an auxiliary exhaust blower located about 100 feet from the working face in a duct which extends to within about 10 feet of the mine face. The blower creates a negative pressure in the duct which withdraws air, methane, dust and the like from the vicinity of the mine face. As the air is routed out of the mine the dust settles and creates an explosion hazard. Rock dust must be added to the dust discharged from the ventilation duct to ensure that the incombustible content of the combined dust is reduced to a safe value. Rock dusting is not an ideal dust treating procedure and several dust collection methods have been developed in an effort to capture the combustible dust from the air as an alternative to rock dusting.
None of these alternative methods has proven satisfactory. For example, one such method employs a bank of screened venturis, within the air duct, and utilizes upstream water sprays to create water droplets, which mix with the air and dust and are wet-impinged on the surfaces of the venturi tubes. The dust particles mix with the water to form a slurry which is ejected by way of a scavenging duct. There are serious problems with this method resulting from excessive dust packing causing build-up on the screens, blockage of the scavenging duct and the plugging of the spray nozzles.
One known method of dry dust removal provides apparatus utilizing a duct stage which includes a plurality of helical turns of the duct itself within an accommodating dust collector hopper, the resulting centrifugal motion imparted to the air providing the dust separation means. Another method provides apparatus which diverts air from a main stream duct into concentrator and separator stages and utilizes an auxiliary blower to return air to the main stream. Neither apparatus utilizes successive banks of venturi units. Another method utilizes a single stage bank of cyclone tubes through which dust-laden air is drawn but does not envisage the diversion of a portion of the air carrying a concentration of the dust for treatment.
No apparatus in the known prior art reveals an apparatus providing a dry dust collection means having the features disclosed herein.